Plants Won’t Help Reduce Greenhouse Gas As Much As Hoped, U of M Study Finds

By Dennis Lien, Pioneer Press, St. Paul, Minn.

Apr. 12–Carbon dioxide-absorbing plants can’t take in nearly as much of the heat-trapping gas as scientists had hoped without artificial boosts of nitrogen, a new study led by a University of Minnesota researcher has found.

Because carbon dioxide is the most common greenhouse gas causing higher surface and atmospheric temperatures, Peter B. Reich said that finding raises the possibility of accelerated global warming.

Until now, worldwide computer modeling has counted on terrestrial plants to use up a good share of the extra carbon dioxide that’s being emitted into the atmosphere, largely by the burning of coal, oil, and natural gas. But the six-year study found that for plants to absorb extra carbon dioxide, they would need artificially higher levels of the nutrient nitrogen, something much of the world’s soils cannot provide.

“This suggests a less optimistic scenario for how much of the elevated CO2 the plant systems can soak up,” said Reich, a professor in the department of forest resources.

The study is the first long-term look at how soil nitrogen affects the abilities of long-lived plants in realistic open-air ecosystems to increase their size by absorbing extra carbon dioxide. It will be published in the April 13 issue of Nature.

In their work at the Cedar Creek Natural History Area north of the Twin Cities, the researchers found that unless plants were given extra nitrogen, there were limits on how much more they could grow, regardless of how much carbon dioxide was available to them.

Much of the world’s soils have limited nitrogen levels, and Reich said it would be impractical to boost those levels to any degree.

The researchers did their study by tending 296 field plots containing different numbers and combinations of perennial grassland species. They subjected each to one of four conditions: some got added soil nitrogen, others got added atmospheric carbon dioxide, and still others got added levels of each. The rest got standard levels of nitrogen and carbon dioxide.

Researchers measured the amount of plant material produced in each setting. After four to six years, plots receiving more nitrogen absorbed at least three times as much extra carbon under higher carbon-dioxide conditions than did plots without any extra nitrogen.

Dennis Lien can be reached at dlien@pioneerpress.com or 651-228-5588.

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